1. Field of the Invention
Embodiments of the invention generally relate to removing material from a substrate. More particularly, embodiments of the invention relate to polishing or planarizing a substrate by electrochemical mechanical polishing.
2. Description of the Related Art
In the manufacture of integrated circuits, layers of conductive material are sequentially deposited on a semiconductor wafer and removed to produce a desired circuit on the wafer.
Chemical Mechanical Processing (CMP) is a technique used to remove conductive materials from a semiconductor wafer or substrate surface by chemical dissolution while concurrently polishing the substrate with downforce and mechanical abrasion. Electrochemical Mechanical Processing (ECMP) is a recently developed variation of CMP which implements an electrochemical dissolution while concurrently polishing the substrate with a reduced downforce. Electrochemical dissolution is typically performed by applying a bias to the substrate surface performing as an anode, and applying a bias to a cathode to remove conductive materials from the substrate surface into a surrounding electrolyte. The bias may be applied to the substrate surface by a conductive material disposed on, or a conductive contact disposed on or through, a polishing material upon which the substrate is processed. The polishing material may be, for example, a processing pad disposed on a platen. A mechanical component of the polishing process is performed by providing relative motion between the substrate and the polishing material that enhances the removal of the conductive material from the substrate. ECMP stations may generally be adapted for deposition of conductive material on the substrate by reversing the polarity of the bias applied between the substrate and an electrode.
The substrate typically begins the planarization process having bulk conductive material deposited thereon in a non-planar orientation, which may be removed by one or more CMP, ECMP, or combination CMP/ECMP processes. When more than one process is utilized, the bulk removal is designed to produce a high removal rate and produce a substrate surface that is substantially planar before going to the next process (e.g., residual removal). In some processes, various chemistries have been developed to promote a higher removal rate of conductive material with lower downforce applied to the substrate. For example, passivation chemistry promotes a higher removal rate on raised areas of the substrate surface by passivating the conductive material on recessed areas of the substrate, thereby producing a more planar surface after the bulk removal process.
The processing pad performing bulk and residual removal must have the appropriate mechanical properties for substrate planarization while minimizing the generation of defects in the substrate during polishing. Such defects may be scratches in the substrate surface caused by raised areas of the pad or by polishing by-products disposed on the surface of the pad, such as accumulation of conductive material removed from the substrate precipitating out of the electrolyte solution, abraded portions of the pad, agglomerations of abrasive particles from a polishing slurry, and the like. The polishing potential of the processing pad generally decreases during polishing due to wear and/or accumulation of polishing by-products on the pad surface, resulting in sub-optimum polishing qualities.